In the late 23rd and 24th century, alien races believed to be on the brink of developing advanced technologies would often be observed by Federation specialists in order to better understand the cultures in advance of first contact. These observations were conducted by nearby bases in system, from duck blind posts or by placing surgically-altered observers within the local population. (TOSnovel: Prime Directive; TNGepisodes: "Who Watches the Watchers?", "First Contact")

It should be noted that first contact does not necessarily represent an actual first encounter so much as the opening of relations (or, in the worst case, hostilities). For example, Earth and Federation Starfleet ships had several rogue encounters with the Ferengi prior to formal first contact in 2364. Another example was the case of exiled Cardassian poet Iloja of Prim, who eventually settled on Vulcan decades before the Federation and the Cardassians first started to interact.

Numerous sources offer different explanations on Vulcan's first contact with Earth. The FASA RPG states that Earth was already exploring space when one of their Franklin series probes discovered a Vulcan colony whilst Strangers from the Sky states that the UNSS Amity discovered a disabled Vulcan craft near the orbit of Neptune which became the source of first contact between the two races.